The invention relates to a process for the recovery of .epsilon.-caprolactam from a reaction mixture of .epsilon.-caprolactam and sulphuric acid, in which the sulphuric acid is removed in the presence of water by reaction with ammonia.
Reaction mixtures containing .epsilon.-caprolactam and sulfuric acid result from the commercial process of preparing the lactam by the Beckmann rearrangement of cyclohexanone oxime to .epsilon.-caprolactam by treating the oxime with sulphuric acid, oleum or sulphur trioxide, as well as in the preparation of .epsilon.-caprolactam by reaction of cyclohexane-carboxylic acid, or a derivative thereof, with a nitrosating agent in the presence of sulphuric acid. To recover the caprolactam from said reaction mixture, the mixture may be treated with ammonia water in a neutralizer to form a supernatant lactam layer and a bottom layer consisting of a concentrated ammonium sulphate solution, after which the two layers are separated and processed as, for instance, in U.S. Pat. No. 2,605,261.
Alternatively, these reaction mixtures can be neutralized under pressure in the presence of ammonium sulphate crystals and a recycled ammonium sulfate-containing mother liquor; the mother liquor is the aforementioned bottom layer containing ammonium sulphate from which solid ammonium sulfate has been removed, as described in applicants' U.S. pat. application Ser. No. 482,601 now U.S. Pat. No. 3,907,781. The heat of neutralization released is utilized to convert water into steam. Preferably, this conversion is effected at a pressure of between 1 and 2 atmospheres, because the use of a higher pressure would require a higher temperature and would result in higher lactam losses due to increased hydrolysis.